In the microelectronics industry as well as in other industries involving construction of microscopic structures (e.g. micromachines, magnetoresistive heads, etc.), there is a continued desire to reduce the size of structural features. In the microelectronics industry, the desire is to reduce the size of microelectronic devices and/or to provide greater amount of circuitry for a given chip size.
Effective lithographic techniques are essential to achieving reduction of feature sizes. Lithography impacts the manufacture of microscopic structures not only in terms of directly imaging patterns on the desired substrate, but also in terms of making masks typically used in such imaging. Typical lithographic processes involve formation of a patterned resist layer by patternwise exposing the radiation-sensitive resist to an imaging radiation. The image is subsequently developed by contacting the exposed resist layer with a material (typically an aqueous alkaline developer) to selectively remove portions of the resist layer to reveal the desired pattern. The pattern is subsequently transferred to an underlying material by etching the material in openings of the patterned resist layer. After the transfer is complete, the remaining resist layer is then removed.
The resolution capability of lithographic processes is generally a function of the wavelength of imaging radiation, the quality of the optics in the exposure tool and the thickness of the imaging layer. As the thickness of the imaging resist layer increases, the resolution capability decreases. Thinning of a conventional single layer resist to improve resolution generally results in compromise of the etch resistance of the resist which is needed to transfer the desired image to the underlying material layer. In order to obtain the resolution enhancement benefit of thinner imaging layers, multilayer lithographic processes (e.g., so-called bilayer process) have been developed. In multilayer lithographic processes, a so-called planarizing underlayer is used intermediate between the imaging resist layer (typically a silicon-containing resist) and the underlying material layer to be patterned by transfer from the patterned resist. The underlayer receives the pattern from the patterned resist layer, and then the patterned underlayer acts as a mask for the etching processes needed to transfer the pattern to the underlying material.
The imaging layer of a bilayer or multilayer resist process typically uses a silicon-containing acid-sensitive polymer. The silicon content acts to provide differential etch characteristics relative to the planarizing underlayer (which is typically free of silicon). Typically, the silicon-containing resist polymer contains at least about 5 or 6 wt. % silicon.
In addition to having significant silicon content, the imaging layer resist composition must also possess the desired lithographic performance with the imaging radiation of interest. With the continued move toward higher resolution lithography, the imaging radiation of interest is quickly becoming 193 nm wavelength (ArF) ultraviolet radiation and is expected to become 157 nm (F2) ultraviolet radiation. Thus, the respective silicon-containing resists for use at these wavelengths must possess desirable optical characteristics and dissolution behavior (i.e., selective dissolution of exposed areas) to enable image resolution at a desired radiation wavelength. Given the extensive experience in the lithographic arts with the use of aqueous alkaline developers, it is important highly desirable to achieve appropriate dissolution behavior in such commonly used developer solutions. A key indicator of the quality of overall imaging performance is so-called line-edge roughness (LER). Thus, it is desirable to obtain silicon-containing resist formulations which provide patterned resist structures exhibiting reduced line-edge roughness.
The general approach in developing resist for bilayer applications has largely been to place the required silicon content on the acid-sensitive imaging polymer. This approach often leads to the need to totally redesign the resist polymer and/or to incorporation of so much silicon-containing moiety on the polymer that the lithographic performance of the resist becomes less than desired. Thus, there is a desire for silicon-containing resist formulations that do not require as much silicon-content on the polymer component of the resist.
The invention provides silicon-containing resist compositions which are capable of high resolution lithographic performance, especially in bilayer or multilayer lithographic applications using 193 nm or shorter wavelength imaging radiation. The resist compositions of the invention are generally characterized by the presence of (a) an acid-sensitive imaging polymer, (b) a radiation-sensitive acid generator, and (c) a non-polymeric silicon additive.
In one aspect, the invention encompasses a silicon-containing resist composition comprising:
(a) an acid-sensitive imaging polymer,
(b) a radiation-sensitive acid generator, and
(c) a non-polymeric silicon additive.
The imaging polymer is preferably useful in 193 nm lithographic processes and preferably contains a monomer selected from the group consisting of a cyclic olefin, an acrylate and a methacrylate. The resist composition preferably contains at least about 5 wt. % silicon based on weight of the imaging polymer. The non-polymeric silicon additive contains at least about 10 carbon atoms, more preferably at least about 12 to 30 carbon atoms. The non-polymeric silicon additive preferably has a molecular weight of about 250 to 1000.
In another aspect, the invention encompasses a method of forming a patterned material structure on a substrate, the material being selected from the group consisting of semiconductors, ceramics and metals, the method comprising:
(A) providing a substrate with a layer of the material,
(B) forming a planarizing layer over the material layer,
(C) applying a resist composition over the planarizing layer to form a resist layer, the resist composition comprising:
(a) an acid-sensitive imaging polymer,
(b) a radiation-sensitive acid generator, and
(c) a non-polymeric silicon additive.
(D) patternwise exposing the substrate to radiation whereby acid is generated by the radiation-sensitive acid generator in exposed regions of the resist layer by the radiation,
(E) contacting the substrate with an aqueous alkaline developer solution, whereby the exposed regions of the resist layer are selectively dissolved by the developer solution to reveal a patterned resist structure,
(F) transferring resist structure pattern to the planarizing layer, by etching into the planarizing layer through spaces in the resist structure pattern, and
(G) transferring the structure pattern to the material layer, by etching into the material layer through spaces in the planarizing layer pattern.
The etching of step (G) is preferably reactive ion etching. The imaging radiation preferably has a wavelength of about 193 nm. The substrate is preferably baked between steps (D) and (E).
These and other aspects of the invention are discussed in further detail below.